The present invention relates to a method of judging plasticization of steel.
When steel such as steel frames used in a construction as a structural body is given an overload exceeding a yield point, plastic deformation is caused. When the plastic deformation is large, it is possible to know the plasticization of the steel through macroscopic observation or dimensional measurement. However, when the plastic deformation is small, since the amount of deformation of the structure is small, or the plastic deformation is concealed by interior materials or fireproof covering materials covering the steel (steel frame), it is difficult to know the existence of the plastic deformation.
In a construction having suffered damages by a big earthquake, it is important to judge whether the structural material was deformed within the range of elastic deformation, or whether it was given a load exceeding the yield point and was plasticized, when considering the continuous usage of the construction and such measures as necessity of reinforcement. However, there was conventionally only a method of indirect judgement from observation of a deformed state of the construction or observation of damages of interior and exterior materials, that is, there were no effective and suitable technical methods which could directly measure the plasticization of the construction.
Incidentally, as metallurgical methods of judging the plasticization of steel, there are known methods in which the constitution of steel is observed to observe dislocations or slip lines generated in accordance with the plasticization, and the surface of the steel is oxidized(etched) to macroscopically observe a distorted hardened region. However, in order to observe the constitution, it is necessary to pick a sample for observation from the steel and to grind the surface. In the case of observation through etching, after heating the steel to a temperature of 250-300.degree. C., it is necessary to conduct etching by a corrosive liquid. Accordingly, although both methods can be applied to a small test piece in a laboratory, both are difficult to be applied to a real construction. Further, there has been investigated a method in which a sample is arranged in a detection coil, an alternating voltage is applied to the coil, and the characteristics of alternate current magnetization is detected, whereby the plasticization of the sample is judged (for example, see Japanese Patent Unexamined Application No. HEI 6-109412). However, also in this case, it is impossible to apply the method to a real construction like the above described metallurgical methods.
In view of the above circumstances, an object of the present invention is to provide an effective method of judging plasticization of steel used in a real construction in a nondestructive manner and with ease.